Mayweather is the strong favourite but Holm, who will face Brazil's Bethe Correia in Singapore, said fights can be unpredictable.
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Mayweather retired after he defeated Andre Berto two years ago, and he said he would only return to boxing for a fight that would make him at least $100 million.
"I talked to him this morning, he wants to fight Floyd Mayweather on August 26, and he wants to defend his title this year too", White said on Wednesday.
However, in what appeared to be a swipe at his opponent's age, he instead posted a photo of Mayweather's father, Floyd Mayweather Sr. Speculation has the two fighters earning approximately $175 million combined for the bout.
According to UFC President Dana White, the answer is - so far, and for now - yes.
"Conor McGregor, when he steps in there, his stand-up game, I'm very damn impressed with it", Ellerbe said.
Reports suggest that Mayweather could pocket around $100 million and McGregor, $75 million, irrespective of the outcome of the showdown. The fight will be one of the biggest moments in the history of combat sports and figures to be one of the greatest spectacles of all time.
The Irishman became the first UFC fighter to hold two belts simultaneously when he knocked out Eddie Alvarez in NY last November for the lightweight championship.
The latest dream to come true for the ex-Irish plumbing apprentice is a mega-money boxing bout against none other than Floyd Mayweather Jr.
"You talk about a guy of Floyd Mayweather's value in the sport, the lawsuit if that ever happened - Conor likes money and Conor would depart with a lot of money if that ever happened". Oscar De La Hoya has called it a farce and said it will harm boxing regardless of the result. It would be a joke, it would be an embarrassment for boxing if an MMA fighter were to go into the ring, it would be a no contest.
"This is an unprecedented event".
It's insane to think, but McGregor was merely a blip on the UFC radar just a few years ago, trying to make it as an up-and-coming fighter from Dublin.